1. Field of the Invention
The present invention relates to an adaptive vehicle speed control system capable of performing a so-called xe2x80x9cfollowing controlxe2x80x9d function according to which a host vehicle can follow a preceding vehicle, while maintaining the host vehicle""s distance from the preceding vehicle at a desired preset inter-vehicle distance, and specifically to the improvement of an automatic speed-control technology containing a following control function as well as a constant-speed control function.
2. Description of the Prior Art
In recent years, there have been proposed and developed various automatic speed-control technologies. An adaptive vehicle speed control system, capable of executing a following control function and a constant-speed control function, has been disclosed in Japanese Patent Provisional Publication No. 8-192662. The adaptive vehicle speed control system disclosed in the Japanese Patent Provisional Publication No. 8-192662 includes an operation switch serving as a man-machine interface and outputting a start command signal needed to initiate the following control function and constant-speed control function, and an electronic control unit (ECU) equipped with a processor. The processor includes a first vehicle speed setting section and a second vehicle speed setting section. The first vehicle speed setting section sets, during a constant-speed control mode, a set vehicle speed at a vehicle road speed the vehicle was traveling at when the start command signal was output. And the second vehicle speed setting section sets, during a following control mode, a set vehicle speed at a predetermined value higher than the vehicle road speed the vehicle was traveling at when the start command signal was output.
However, the adaptive vehicle speed control system as disclosed in the Japanese Patent Provisional Publication No. 8-192662, has the following drawback.
For instance, when a start command signal for initiation of the constant-speed control mode is output under a particular condition where the vehicle slows down owing to the braking action and then is still running at an excessively low speed but not yet stopped, the set vehicle speed may be set to such an excessively low speed. Thereafter, the brakes tend to apply automatically each time the limiting action of the vehicle speed to the excessively low speed (determined as the set vehicle speed) occurs. As can be appreciated, owing to the set vehicle speed set to such an excessively low speed, there is an increased tendency for the braking action to undesiredly continue so as to maintain the set vehicle speed at the excessively low speed, and thus the driver/vehicle occupants may feel uncomfortable.
Accordingly, it is an object of the invention to provide an adaptive vehicle speed control system, which avoids the aforementioned disadvantages of the prior art.
It is another object of the invention to provide an adaptive vehicle speed control system capable of avoiding a vehicle-speed limiting action based on undesirable braking action, even when an adaptive vehicle speed control is engaged during vehicle driving at an excessively low speed less than a predetermined low-speed threshold value. order to accomplish the aforementioned and other objects of the present invention, an adaptive vehicle speed control system comprises a vehicle speed detection device which detects a host vehicle speed of a host vehicle which is subjected to adaptive vehicle speed control including preceding vehicle following control and vehicle speed control, an inter-vehicle distance detection device which detects an inter-vehicle distance between the host vehicle and a preceding vehicle ahead of the host vehicle, a set-vehicle-speed setting device having a man-machine interface for setting a set vehicle speed, a vehicle speed controller comprising a desired inter-vehicle distance arithmetic-processing section calculating a desired inter-vehicle distance based on at least the host vehicle speed, a following control section determining a desired speed of the host vehicle based on the host vehicle speed and the inter-vehicle distance so that the inter-vehicle distance is brought closer to the desired inter-vehicle distance in presence of detection of the preceding vehicle, and a vehicle-speed adjustment device which adjusts the host vehicle speed to the desired speed determined by the vehicle speed controller, and an adaptive-vehicle-speed-control initiation command device which outputs a command signal indicative of initiation of the adaptive vehicle speed control including the following control performed through the following control section and the vehicle speed control performed through the vehicle speed control section, wherein the vehicle speed controller includes a vehicle speed setting section which sets the desired speed determined by the vehicle speed controller to a speed value higher than a low-speed threshold value, in presence of output of the command signal under a specified condition where the host vehicle speed is below the low-speed threshold value.
According to a further aspect of the invention, an adaptive vehicle speed control method, which comprises detecting a vehicle speed of a host vehicle which is subjected to adaptive vehicle speed control including preceding vehicle following control and vehicle speed control, detecting an inter-vehicle distance between the host vehicle and a preceding vehicle ahead of the host vehicle, setting a set vehicle speed through a man-machine interface, calculating a desired inter-vehicle distance based on at least the host vehicle speed, determining a desired speed of the host vehicle based on the host vehicle speed and the inter-vehicle distance so that the inter-vehicle distance is brought closer to the desired inter-vehicle distance in presence of detection of the preceding vehicle, adjusting the host vehicle speed to the desired speed, outputting a command signal indicative of initiation of the adaptive vehicle speed control including the following control and the vehicle speed control, and setting the desired speed to a speed value higher than a low-speed threshold value, in presence of output of the command signal under a specified condition where the host vehicle speed is below the low-speed threshold value.